Introduction to Servlet API
The Java Servlet API is an acronym for Application Programming Interface (API) that is used on a server to interact with the other pages. It communicates with the clients through a request and response format or system in a servlet container. An application programming interface (API) for servlets is a group of predefined packages, classes, and interfaces that have been written, along with their servlet methods and constructors. It is a mechanism for interaction between two web application components and servlet functions.
- The servlet API is an essential part of the servlet lifecycle in all web and desktop applications.
- It makes it easy to create an application for all developers.
- It provides several functions and packages.
- It provides several methods in a single API.
- It helps to connect with other software applications also.
What is Servlet API?
Servlets are Java pieces of code on a web server or server-side that can handle Java.
We can manage the request from the remote server, process and operate the servlet request, make the servlet response, and then return the web page or server.
We can also use Servlets to make several web or Java-based applications. It must utilize the Servlet API, which includes all virtual interfaces and classes, to make Java Servlets.
Servlet API comes in two packages, which are:
The servlet pages or web container uses many interfaces and classes from the “javax.servlet” package. The “javax.servlet.http” package has classes and interfaces that manage http requests.
Servlet API Interfaces in the Package
The servlet API interfaces are used in the servlet technology packages for web applications. We can see the interfaces with detailed information.
1. javax.servlet.http package
The following Servlet API interfaces use in the “javax.servlet.http” package.
- HttpServletRequest: To deliver servlets details about HTTP client requests. It uses the servlet interface, which is ServletRequest.
- HttpServletResponse: To send a response to a service user in a way that works with HTTP. It uses the servlet interface, which is ServletResponse.
- HttpSession: It gives a way to keep track of information about a user across an application or website’s webpage and identify that client.
- HttpSessionActivationListener: The container uses to tell all the objects connected to a session, and the session will be turned off and then turned on.
- HttpSessionAttributeListener: This listener interface can be used to find out when changes are made to the attribute lists of sessions in this web application.
- HttpSessionBindingListener: It tells a HttpSessionBindingEvent object to send information or a message to an object when that object is bound to the session or unbound from a session.
- HttpSessionListener: When something changes in a web page or application’s list of active sessions, the interface gets notified.
2. javax.servlet package
The following several Servlet API interfaces use in the “javax.servlet” package:
- Filter: To filter the request to a resource, the response from it, or both functions.
- FilterChain: To show the developer how a filtered request for a resource went through the invocation chain. This is done by the servlet container.
- FilterConfig: To send information to a filter when a servlet container starts up.
- RequestDispatcher: It makes an object that sends the request and response to any other resource. This means it takes requests from the client and sends them to a servlet, HTML file, or JSP file on the server.
- Servlet: This primary interface tells all servlets what methods they must implement. Write a generic servlet that extends javax.servlet to use this interface. GenericServlet or a servlet for HTTP that extends javax.servlet. http.HttpServlet.
- ServletConfig: It describes an object created by a servlet page when a servlet is instantiated and is used to send information to the servlet when it is initialized.
- ServletContext: It describes a group of methods that a servlet can use to talk to its servlet container. The ServletContext object is where the information in the web.xml file about the web application is kept.
- ServletContextAttributeListener: The classes use this interface when the attribute list of a web application’s servlet context changes.
- ServletContextListener: The classes that use this interface are told when the servlet context of the web application they are a part of changes.
- ServletRequest: It describes an object a servlet container makes to pass information about a client’s request to a servlet.
- ServletRequestAttributeListener: Let the listener know when a request attribute changes while the request is in the scope of the web application where the listener is registered.
- ServletRequestListener: Let a web component know when requests come in and leave its scope.
- ServletResponse: It describes an object a servlet container makes to help a servlet send a response to a service user.
Given below are the FAQs mentioned:
Q1. What are the servlet API’s two classes?
Answer: The javax.servlet must be used by every servlet page or API. Most servlets API do this by extending either javax.servlet.GenericServlet or javax.servlet.http.HttpServlet, which are special classes.
Q2. What’s the difference between a package and a Servlet API?
Answer: The package is a collection of files or classes that can contain an operational program. In the situation you gave in the question, a Servlet API is a way to get data from the web server for the servlet page.
Q3. Write the difference between the servlet API and interface.
Answer: It stands for “Servlet Application Programming Interface,”. Servlet Interface is part of the API’s name. One type of servlet interface is a servlet API, but not every interface is an API.
Q4. What is the most up-to-date version of the servlet API?
Answer: The last version of the Java Servlet API is version 2.1. It is usable for all Java Servlet specifications.
It is an advanced function to use in web applications. It is a group of methods, classes, packages, and interfaces to operate functionality at a time. It helps to reduce the coding size of the programmer.
This is a guide to Servlet API. Here we discuss the introduction, servlet API interfaces in the package and FAQs respectively. You may also have a look at the following articles to learn more –